1. Field of the Invention
The present invention relates to a drill screw for enabling itself to anchor in a threaded hole produced in a metal panel by its own.
2. Description of the Prior Art
In general drilling screws or merely drill screws are known, which have a drill section in the male thread portion. This conventional drill screw can make a threaded hole in the panel with its drill section when it is screwed into the panel. In this way by a single drive drilling, tapping and anchoring are simultaneously performed.
To explain the background of the invention more in detail, reference will be made to FIG. 4:
The illustrated screw is provided with a drilling section (D), which has grooves 13 each forming rake surfaces. In addition the screw has a web 11 whose top is shaped like a dome. The reference numeral 12 denotes cutting edges. The screw is driven into a metal panel by means of an electric driver. As a result a hole is produced by the cutting edges 12 of the screw. However, the central part of the hole is left from cutting because the web 11 is placed in abutment with the central part. The web has no cutting ability. The web 11 is forced into the hole under thrust. Because of the cutting incapability of the web the screw as a whole undergoes a great frictional resistance from the side walls of the hole. The degree of resistance depends upon the hardness of the panel, and the width of the web. This results in the inefficient drilling operation.
The present invention is directed to solve the problems pointed out with respect to the known drill screws, and has for its object to provide an improved drill screw whose web has a cutting ability so as to enhance the efficiency of drilling operation.
Other objects and advantages of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific embodiment are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
According to the present invention, there is provided a drill screw, which comprises a web on top of the drilling section, the web having an elongated recess in its central portion, wherein the recess is defined by two chisel edges each rising toward the respective ridges, thereby forming a dome-like web.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.